Published online by Cambridge University Press: 14 August 2015
The Tycho Catalogue contains astrometric and photometric data for the one million brightest stars on the sky. About 900000 stars are high quality astrometric reference stars. Photometry in a blue and visual band is provided.
Two extensions of the catalogue are under way. One is the extension to one magnitude fainter stars by a second reduction of the original Tycho observations, resulting in a catalogue with a total of about three million stars. The other extension is the derivation of more accurate proper motions by means of the Astrographic Catalogue positions as first epoch. This latter work will be carried out first for the one million stars, and later for all the three million, resulting in the Tycho Reference Catalogue (TRC).